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Modeling Tool
Advances Rotorcraft Design
Transportation
Originating Technology/NASA
Contribution
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CHARM
is a computer software product that models the
complete aerodynamics and dynamics of rotorcraft in
general
flight conditions. |
Often times, when people think of NASA, they think of space
travel. The first “A” in NASA, however, is for “Aeronautics,”
and the Agency has always held as one of its tenets to
explore, define, and solve issues in aircraft design. Just
as often as NASA is associated with space travel, when
people hear aeronautics, they often think of airplanes,
but part of NASA’s aeronautics program is one of the most
advanced rotorcraft design and test programs in the world.
Located at Ames Research Center, the Aeromechanics Branch
of the Flight Vehicle Research and Technology Division
conducts theoretical and experimental research in support
of the U.S. helicopter industry and the
U.S. Department of Defense. At this research site, engineers
study all aspects of the rotorcraft that directly influence
the vehicle’s performance, structural and dynamic responses,
external acoustics, vibration, and aeroelastic stability.
They use modern wind tunnels and advanced computational
methodologies to calculate fluid dynamics and perform multidisciplinary,
comprehensive analyses in the quest to further understand
the complete rotorcraft’s operating environment and to
develop analytical models to predict aerodynamic, aeroacoustic,
and dynamic behavior. The experimental research also seeks
to obtain accurate data to validate these analyses, investigate
phenomena currently beyond predictive capability, and achieve
rapid solutions to flight vehicle problems.
Partnership
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CHARM
represents the culmination of over 25 years of continuous
development of rotorcraft modeling technologies at
Continuum Dynamics Inc., and incorporates landmark
technical achievements from a variety of NASA, U.S.
Department of Defense, and company-sponsored initiatives. |
Founded in 1979, Continuum
Dynamics Inc. (CDI), of Ewing,
New Jersey, specializes in advanced engineering services,
including fluid dynamic modeling and analysis for aeronautics
research. Its clients include government agencies, as well
as the aerospace, nuclear, and pharmaceutical industries,
and it has been partnering with NASA since its inception.
The company has converted years of NASA-funded research
efforts into a variety of commercial products. For example,
1987 and 1992 NASA Small Business
Innovation Research (SBIR) grants on helicopter wake modeling resulted in software
code used in a blade redesign program for Carson Helicopters,
of Perkasie, Pennsylvania, that simultaneously increased
the payload of its Sikorsky S-61 helicopter by 2,000 pounds
and increased cruise speeds at 10,000 feet by 15 knots.
Follow-on development of this same rotorcraft model, based
on 1999 and 2002 NASA SBIR work, resulted in a $24 million
revenue increase for Sikorsky Aircraft Corporation, of
Stratford, Connecticut, as part of the company’s rotor
design efforts.
Altogether, the company has completed a number of SBIR
projects with NASA, including early rotorcraft work done
through Langley Research Center, but more recently, out
of Ames.
This rotorcraft model software code, marketed by CDI as
the Comprehensive Hierarchical Aeromechanics Rotorcraft
Model (CHARM), is a tool for studying helicopter and tiltrotor
unsteady free wake modeling, including distributed and
integrated loads, and performance prediction.
Product Outcome
Under continuous development at CDI for more than 25 years,
CHARM analyzes the complete aerodynamics and dynamics of
rotorcraft in general flight conditions. CHARM has been
used to model a broad spectrum of rotorcraft attributes,
including performance, blade loading, blade-vortex interaction
noise, air flow fields, and hub loads. The highly accurate
software is currently in use by all major rotorcraft manufacturers,
NASA, the U.S. Army, and the U.S. Navy.
Available as a stand-alone product or adaptable to existing
simulator and analysis systems, this software code is well
suited for performing analysis on advanced aerodynamic
design as well as for research on new designs. The software
includes extensive 3-D graphics capabilities that allow
highly detailed visualization of the rotor/wake motion
and wake/surface interaction. Easy to use and reliable,
CHARM plugs directly into alternate rotorcraft analysis
or flight simulation software.
CHARM incorporates one of the most advanced wake models
currently available, combining a full-span, freely distorting,
constant vorticity contour wake model and an analytical
tip vortex roll-up model to provide accurate wake simulation.
Without the software, designers would have to guess the
proper empirical constants in order to approximate wake
characteristics.
According to CDI, the new fast vortex and fast panel technologies
implemented within CHARM provide a great advancement in
computational performance when compared to existing panel
codes currently available. This increased performance allows
the designer to explore high-risk technologies, expand
design parameter ranges, and evaluate critical components
at a level of detail never before possible.
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CHARM
is available for licensing as a stand-alone analysis
program or as a module that couples directly into
existing flight simulation or analysis software. |
According to CDI, CHARM features the most advanced free
vortex wake model currently available that directly computes
wake roll-up and vortex core properties from first principles.
In addition, no empirical constants are required, which
is a distinct advantage for design work and modeling transient
maneuvering flight for which wake characteristics are continually
changing. The software code has also been coupled with
acoustic prediction software to provide fast prediction
of rotor loading and thickness noise.
CHARM’s lifting surface blade aerodynamics model is well
suited for analysis of complex tip shapes and other 3-D
effects, and its coupled wake/panel calculation
is unique—incorporating state-of-the-art fast vortex and
fast panel methods to allow fully coupled rotor/wake/airframe
solutions.
Most recently, the software has been incorporated into
a joint CDI-Army study for incorporation into flight simulation
software to practice landing rotorcraft in sandy or dusty
conditions. Known as brownout, the effect of sand, dust,
and debris kicked up by a helicopter during takeoff and
landing can temporarily blind a pilot, as well as damage
moving parts. The simulator is designed to identify, characterize,
and evaluate brownout conditions for general aircraft,
wind, ground topology, and flight maneuvers. The study
seeks to improve pilot training for these dangerous conditions,
help in mission planning, decrease damage to rotorcraft
components, and improve sensor technologies most affected
by these conditions.
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